The present invention relates generally to a method and apparatus for resecting a long bone, and more particularly, to a method and apparatus for preparing the distal end of the femur and the proximal end of the tibia to receive a prosthetic knee joint.
A natural joint in the human body such as a knee joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become advanced and are irreversible, it may ultimately become necessary to replace the natural joint with a prosthetic joint. Such a prosthetic joint often includes several biocompatible components which are formed from high strength synthetic materials. These materials are not only able to accommodate the various loading conditions that the prosthetic joint may encounter, but are also biocompatible with the human body.
The effective reinstatement of natural joint functioning through use of a joint prosthesis depends on the combined influences of component features and accurate anatomical positioning of the components. The positioning factor makes the instruments, and their sequence of application, keys to achieving natural joint functioning. The instruments aid in the making of proper cuts of the appropriate portions of the bones in preparation of receiving the prosthetic joint components and also have utility in correctly aligning the angle of the cuts relative to the bone.
Initially, it is necessary that the distal end of the femur be appropriately cut so as to receive the prosthetic femoral component. According to one approach for resecting the distal end of the femur, the anterior surface of the distal end of the femur is first resected. Once the anterior surface is resected, the distal femur osteotomy is performed. Thereafter, the posterior femoral osteotomy is made to resect the posterior surface of the femur. Chamfer cuts are next made intersecting both the flat surfaces of the distal femur and the anterior femur and the flat surfaces of the distal femur and the posterior femur. Once the anterior, posterior, and distal osteotomies and the chamfer cuts are made, the distal end of the femur is reamed to receive the biocompatible femoral component of the prosthetic joint.
Similarly, the proximal end of the tibia must also be prepared to receive a biocompatible component. A proximal tibia osteotomy is undertaken to resect the proximal tibial surface. Axial reaming is also required to prepare the distal end of the tibia to receive a biocompatible tibial component.
The surgical steps necessary to prepare the distal end of the femur and the proximal end of the tibia for receiving their respective prosthetic components are inherently complex. The procedures are made complex by the fact that careful attention must be paid to the amount of bone being resected, the angles of the cut with respect to each other, and the angles of the cut with respect to the axes of both the femur and the tibia. If either the femoral or the tibial component fail to fit properly, revision surgery may ultimately be necessary.
The proper execution of the resection is the most important aspect in the preparation of a long bone for receiving a prosthetic component. There are many known devices which provide a guide surface for the cutting blade and these devices are typically attached to or positioned in alignment with the bone. The basic forms of these devices include "armless" and "armed" guides. Both forms include a body having a blade-positioning surface. The body is typically a flat-sided block having a flat surface that acts as a saw guide. The body is temporarily attached to the bone during resection. Some variations of the typical block-shaped bodies include bodies having curved walls that wrap partially around the bone. In the "armed" version of known saw guides, a pair of saw guide arms are pivotably and permanently attached to the saw-guide body and partially wrap around the bone.
However, these designs fail to provide a satisfactory guide for resection. Specifically, and with respect to the "armless" devices, these devices typically only provide a small blade-positioning surface, and fail to provide a surface that offers more than 20 or 30 degrees of support around the bone, even where the body is curved. While providing a larger blade-positioning surface, in the "armed" form of the device the arms are pivotably attached to the body in a permanent manner. The arms are formed having the widest possible curvature in an effort by the manufacturer to provide a "universal" saw guide capable of fitting around a bone having a large diameter. The "universal" design allows the saw guide, in theory, to be applied to bones of lesser diameters as well. However, this "one size fits all" construction fails to provide a reliable cutting surface when designed to allow for the largest possible bone to be resected. This is so because the saw blades, which are often only about two inches long and are required to make cuts of about one-and-a-half inches, are not properly supported by a blade-positioning surface that may be positioned some distance from the bone surface. Ideally, the operator would be able to maintain the cut guide in close proximity to the bone to provide support for the blade and to thereby reduce the incidence of improper cuts, blade deflection, and scything. The failure of "one size fits all" guides becomes increasingly acute as the device is applied to bones of decreasing diameters.
Another difficulty encountered by surgeons in the execution of resection is blade control. Many known cutting guide devices provide only limited assistance to the surgeon in controlling movement of the blade. Specifically, the surgeon must reciprocate the blade against the blade-positioning surface while trying to prevent the blade from being lifted off of the surface during cutting. In an effort to overcome this, some guides have incorporated saw blade capture plates that are positioned spaced apart from the saw guide surface, this spacing forming a saw guide slot, the slot being desirable to reduce scything. Hitherto these slots have only been provided on the "armless" saw guides, and, while limiting lateral movement of the saw blade to a certain extent, suffer from the same limited blade-positioning surface of these types of devices.
Accordingly, it is desired to provide a system which allows relatively uncomplicated preparation and resecting of the bone surfaces for adaptation to receive biocompatible components of a knee joint prosthesis.